Why am I going using so much coolant? Having to add coolant every other month? on 1990 BMW 535i

Cannot see any visible leaks from hoses, etc. but resivoir gets low and engine temp rises. Then, car started stalling when I was driving and now EML light is on and car will turn over but not start at all. Tried cleaning up the gas with an fuel cleaner and an octane booster. Are these 2 things related?

Asked by for the 1990 BMW 535i
If it is not leaking on the ground check your oil dipstick to see if the oil is a milky white color. If it is this color the coolant is going in the engine and the car should not be driven to avoid any further damage which will cost you more in repairs. You may be to late though if you can't get it running. First check the dipstick. Most of the time the fuel tratments are used to treat a certain amount of fuel so by adding what you did at the same time could cause a fuel problem but I can't say for sure this may be your problem.